Due date: 04 October 2022
Weighting: 25% (250 marks)
This assessment is designed to test your achievement of selected learning objectives of Modules 6 to 9. In particular, the assignment involves estimation of urban design discharges, reservoir routing and water balance. It is intended to reinforce and extend your knowledge on urban hydrology, using a low density residential subdivision as a case study.
The assignment is divided into three parts:
- Part 1 – Reservoir Routing.
- Part 2 – Estimation of Minor and Major design flows for the urban subdivision
- Part 3 –Water balance analysis .
Part-1: Reservoir Routing
A hypothetical project has been devised to demonstrate how hydrology may be incorporated in engineering practice. Although the project is hypothetical, the various hydrological tasks that are included in the project are representative of what you may encounter after you graduate.
The following is the scope of Part-1 and Part-3 with two separate exercises:
- An investigation of the hydrological impact of the proposed onstream weir on downstream riparian habitats.
- A preliminary water balance analysis of the proposed off-stream aquaculture pond to determine if acceptable water levels can be maintained by Caboolture River streamflows
Hydrological impact of the onstream weir
Description of impact analysis
An Environmental Impact Assessment is required to gain approval for construction of the diversion weir. Discussions with relevant authorities and an aquatic scientist working on the project team suggest that an initial analysis should be performed to quantify the likely hydrological impact of riparian habitats downstream of the proposed weir. The main outcomes of the discussions were:
- The initial analysis can be based on a most recent flood event of February 2022 recorded in the Upper Caboolture River should be used for this purpose
- To assess the potential ecological impact of the proposed weir, the aquatic scientist requested responses to the following questions:
- Would the peak discharge during the selected representative flood significantly change after the weir is built?
- Would the weir significantly prolong the duration of flood inundation of the downstream habitat?
To assist the aquatic scientist, you are tasked with undertaking a reservoir routing analysis to estimate how the February 2022 flood hydrograph may change due to the proposed weir.
Useful materials for impact analysis
A detailed topographic survey of the Upper Caboolture River at the weir site was prepared. From this information, the volume of water able to be stored upstream of the weir at different elevations were computed. The details are:
|Elevation (mAHD)||Storage Volume (ML)|
For the purpose of the initial hydrological analysis, it was decided that the preliminary weir configuration is of 35m long with a crest elevation of 76.0 mAHD. The initial level at the start of the event is considered as 63m.
Methodology for impact analysis
It is recommended that you undertake the following activities to initially evaluate the hydrological impact of the proposed weir:
- Setup an EXCEL spreadsheet to make the necessary reservoir routing computations
- Determine an elevation – storage volume relationship for the proposed weir pondage. It is acceptable to fit a regression equation to the data that has been provided.
- Determine an elevation- outflow discharge relationship based on the weir flow equation for the adopted weir configuration
- Compute a lookup table needed for the reservoir routing analysis
- Undertake the reservoir routing analysis for the February 2022 flood hydrograph. Report the effect of the proposed weir in terms of change in peak discharge and inundation duration.
- Document your analysis in the report.
Part-2: Estimation of Minor and Major design flows for the urban subdivision
Proposed Amberley residential subdivision
A drainage scheme is to be designed for a 28 lot residential located at Amberley, near the city of Ipswich, Queensland. A copy of the subdivision layout plan can be downloaded from Studydesk (Subdivision Lots Layout.pdf). The subdivision includes a network of proposed internal roads (Roads 02, 03 and 04).
Your task is to prepare a Minor system design check of the stormwater system upstream and including Pit 04/01 based on the preliminary layout and then a Major system check. The Minor system is to cater for the 2 year ARI storm and the Major system for the 100 year ARI storm. The system includes stormwater line 1 (pits 01/01 to 04/01) and line 2 (pits 01/02 and 02/02).
Pits will be based on Brisbane City Council standard drawings. Initial surface levels at pit locations are given in Table 1.
Table 1: Initial design details at pit locations
|Pit/Location||Finished Surface Level (m LD)|
LD = Local datum
Use the following information:
- The location of the subdivision is 27.62° S, 152.66° E
- The road kerbs are BCC ‘Type D’ kerb and channel. Roads 03 and 04 will have a 6.5m wide road pavement (kerb to kerb). The width of Road 02 is 8m. All roads have a dual crossfall of 1:30 (i.e. roadway has a central crown). Assume the road reserve is 50% impervious.
- Assume all road pits will be 2400 lintel ‘lip in line’. The pits along Road 02 are on grade and all other pits are in sag. Sag pits have different hydraulic capacities compared to on grade pits due to the effect of water ponding.
- The proposed lots will be developed to ‘low density residential’ with an expected percentage impervious within the lot area of 60%.
- Soil permeability can be classed as ‘Medium’. Pervious parts of the subdivision can be classed as ‘Medium density bush’ or “Good grass cover’.
- Assume no flow of stormwater runoff into lots from neighbouring lots (i.e no flow across shared lot boundaries). Once flow meets an internal shared lot boundary, assume ‘concentrated overland flow’ conditions. Assume flows across lot boundaries to the street can occur. Use the contours shown on the layout plan to identify the subcatchment boundaries draining to each pit. This may mean that the full area of some lots may not drain to the nominated pits.
- To simplify the analysis, assume that there is no stormwater entry to Roads 02, 03 and 04 from external areas outside of the proposed subdivision. It is assumed that there is existing drainage to service the existing main road on the eastern entry to the subdivision. The catchment boundary shown as the red line on the subdivision layout plan can be used on this basis.
- The minimum travel time to a pit is 5 minutes and the maximum is 20 minutes. Reminder: Partial Area check is based on the most remote, directly connected impervious area to the pit. The travel time may be longer than 5 minutes.
- In completing the Hydrologic Design Sheets, it is acceptable to combine together lot subcatchments that have the same fraction impervious, rather than report CA values for individual lots.
- It is acceptable to scale up the CA values based on the frequency factor ratio F100/F2– this will simplify the calculations for the Major Storm analysis
- Do not use standard inlet times
- For pipe flow travel times for Sheet 2, use a minimum pipe gradient of 0.3% otherwise the road slope.
- Gutter flows in the street during the Minor storm should be contained within the full roadway width with zero depth at the crown. The maximum flow depth at the road kerb during the Major storm should contain flooding to within the road reserve. This corresponds to a maximum water depth of 0.25m. dV product should not exceed 0.6 m2/s. At the sag pits, check both the ponded water width at the pit and the roadway flow hazard approaching the pit during the Minor Storm.
- Unless otherwise defined, the drainage design check will be in accordance to the 2017 edition Queensland Urban Drainage Manual which can be accessed from UniSQ library through ezproxy link. Suitable AR&R IFD data can be used to generate design rainfall intensities.
- Undertake the Major design flow check for Road 02 at just downstream of pit 04/01.
Scope of Part-2
The scope of Part 2 is to undertake a Minor and Major analysis of the proposed drainage system by completion of Hydrologic Design Sheets 1, 2 and 3 (as per Module 7 of the Study Book).
After completion of the Design Sheets, review the results and make suggestions on revisions to the proposed road drainage system (e.g. requirement for additional pits, if any). It is not required to reanalyse and update the Design Sheets.
The design sheets shall be supported by:
- A plan showing the boundaries of each pit subcatchment and the flowpath to each pit used in the time of concentration calculation.
- Design assumptions (refer to report template)
- A worked example of how an (arbitrarily) selected row of each design sheet was determined, by providing the calculations in more detail.
- An output summary – giving the pit size at each pit location, the Minor discharge in each pipe reach and the Major flow characteristics (discharge, flow width, dV product) at the selected road location.
Useful Material for Part-2
The following materials have been provided and can be downloaded from StudyDesk or from external websites:
- Subdivision layout base plan
- Gully pit designs and hydraulic capacity charts can be downloaded from http://www.brisbane.qld.gov.au/planning-building/planning-guidelines-and-tools/guidelines/standard-drawings/index.htm
- Final QUDM can be downloaded from Studydesk
- Refer to Bureau of Meteorology website for online IFD tool for design rainfalls.
Part-3: Water balance analysis of a pond
Description of water balance analysis
Your next major task is to undertake a water balance analysis of a pond. For the purpose of the analysis, the following pond configuration applies:
- A trapezoidal-shaped pond with base dimensions of 200m long by 100m wide. Assume that the pond base is flat.
- The pond embankment has an internal batter of 2H:1V on all sides.
- The maximum water depth in the pond is 2m.
A relatively constant water level in the pond is considered desirable for silver perch growth. Below a critical water level of 1.5m, the pond would need to be ‘topped up’ from an alternative water supply at considerable expense. Thus, to establish the overall viability of the aquaculture project, it is considered important to determine the frequency and time duration it is expected that the pond water depth will be below 1.5m.
River water will be pumped from the proposed weir pondage to supply the pond. This will be subject to a water allocation licence and initial discussions with the relevant authority suggest that the pumping of water is expected to be limited by the following pumping rules, based on flows at the weir site:
- No pumping is allowed at Upper Caboolture River discharges of less than 200 ML/d
- For Upper Caboolture River discharges exceeding 200 ML/d, the maximum water extraction shall be 10 ML/day.
The water balance analysis should be performed at a daily timestep and account for the following components:
- Upper Caboolture River streamflows into the proposed weir. These shall be computed using the ‘cut-down’ AWBM described in Module 8. The pumped water from the weir to the pond can then be directly computed from these streamflow estimates based on the pumping rules listed above.
- Evaporation from the pond surface. This water loss can be computed using daily pan evaporation data adjusted by an appropriate coefficient.
- Direct rainfall onto the pond surface. The pond has no land catchment and thus local runoff draining into the pond can be ignored.
- Seepage from the pond bed. Testing of the existing pond site indicates that a seepage loss equivalent to 0.002 m/day is expected to occur. The effect of this water loss is of concern and your analysis should factor in seepage in the pond water balance.
- To simplify the computations, base the evaporation, direct rainfall and seepage estimates on the base area of the pond.
- Pumping to the pond will cease when the full pond capacity is reached.
- For the purpose of the feasibility assessment, provide an analysis of the pond with no topping up.
Hydrological data is available for the 5 year period from 1/3/2017 to 1/03/2022. A water balance analysis would normally be carried out over a longer timeframe, but has been reduced for the purpose of this assignment. The water balance should be performed in an EXCEL spreadsheet to determine the following measures of pond conditions during the 5- year simulation period:
- The number of separate occasions that the pond water depth would be critically low
- The average annual period of time that the pond water depth would be critically low (in days/yr)
- The average annual loss of water due to evaporation and seepage (in ML/yr)
- The average annual pumped extraction of water from the weir (in ML/yr) Useful materials for water balance analysis
- Daily rainfalls at station 142001A can be obtained from Water Monitoring Portal https://water-monitoring.information.qld.gov.au
- The average pan evaporation data is provided below in Table-2. You can consider a constant daily evaporation rate for all the days in a month. A pan coefficient of 0.8 is applicable.
Table 2: Pan Evaporation data (mm/day)
|Month||Pan Evaporation (mm/day)||Month||Pan Evaporation (mm/day)|
Your submission for Assignment 2 should include:
- A detailed report that documents all the tasks required as part of the Assignment-1. A marking scheme is provided as Table 3. Use this marking scheme to check that you have addressed the full scope of the work. If an element of the assignment has not been documented in the file report than no marks will be given for that element.
- An Excel sheet with all the calculations shall be submitted. Electronic submission of the report and excel sheet should be through the study desk.
- Part of the available marks has been allocated to reward reporting that is well set out and easy to follow. Submissions that are untidy and/or poorly structured and thus difficult to assess will attract less marks for this element.
The following filename convention shall be used: YourName_Ass1.pdf and YourName_Ass1.xlsx,where Your Name is your first and last names.
Penalties for late assignment submission:
If an Assignment is submitted after the published deadline without an approved extension of time, the maximum Mark will be reduced as a consequence. In this case, the available Mark is reduced by 5% (of the original available Mark) for each Calendar Day or part day that the Assignment is late.
An Assignment submitted more than one (1) week after the due date will have a Mark of zero recorded.
For students with an approved extension, a zero Mark will be awarded for an Assessment Item if it is submitted after an approved extension date.
Table 3: Assignment 2 Marking Scheme
|Part-1 Reservoir routing|
|Lookup table based on elevation-storage and elevation-discharge relationships||15|
|Correct setup of reservoir routing spreadsheet||20|
|Calculated and plotted hydrographs||10|
|Determination of changes to peak discharge and inundation time||5|
|Part 2 Minor and Major Design Discharges|
|Design assumptions and output summary|
|Catchment plan showing subcatchment boundaries and flowpaths||10|
|Table of pit subcatchment details||5|
|Table of 2 year and 100 year ARI rainfalls||5|
|Table of runoff coefficients||5|
|Izzard table and hydraulic capacity charts||5|
|Output summary table||5|
|Suggestions for revisions to proposed drainage||5|
|Sheet 1 and worked calculation|
|Appropriate time of concentration estimates (Col 1 to 8)||5|
|Full area CA values and Rational Q estimates (Col 9 to 14)||5|
|Partial area CA values and Rational Q estimates (Col 9 to 14)||5|
|Pit inlet analysis and road hazard (Col 15 to 25)||5|
|Sheet 1 worked calculation||5|
|Sheet 2 and worked calculation|
|Full area calculations (Col 1 to 5)||5|
|Partial area calculations (Col 6 to 11)||5|
|Sheet 2 worked calculation||5|
|Sheet 3 and worked calculation|
|Appropriate time of concentration estimates (Col 1 to 8)||5|
|Road Q and capacity check (Col 9 to 18)||10|
|Sheet 3 worked calculation||5|
|Part 3: Water Balance Analysis|
|Selection of AWBM parameters and catchment data||15|
|Computation of runoff using cut-down AWBM for full simulation period||20|
|All water balance components taken into account and modelled||20|
|Computation of pond water balance for full simulation period||15|
|Computation of measures of pond conditions||10|
|Assignment EXCEL spreadsheet||10|
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